Analysis of neurogenesis and programmed cell death reveals a self-renewing capacity in the adult rat brain.

The adult central nervous system was thought to be very limited in its regenerative potential; however, the discovery that stem cell populations produce neurons in the adult brain highlights the dynamics of a previously assumed 'static' organ. The continuous generation of new neurons in the adult brain, nevertheless, leads to the question of whether neurogenesis is counterbalanced by an accompanying cell death in the same regions. The objective of this study was to stereologically analyze neurogenesis and programmed cell death in adult brain regions with known neurogenic activity. Using bromodeoxyuridine (BrdU) to identify newborn cells we find that within a few days of BrdU-labeling the adult dentate gyrus and olfactory bulb generate high numbers of newborn neurons. More importantly, dUTP-nick end labeling (TUNEL) reveals that areas of adult neurogenesis also contain high numbers of apoptotic cells. We conclude that programmed cell death may have an important regulatory function by eliminating supernumerous cells from neurogenic regions and may thus contribute to a self-renewal mechanism in the adult mammalian brain.